Hex Input

<label class="nuda-hexin">
  <span class="nuda-hexin__chip" style="background:#e4ff54"></span>
  <span class="nuda-hexin__hash">#</span>
  <input value="E4FF54" maxlength="6" />
</label>

const wrap  = document.querySelector('.nuda-hexin');
const chip  = wrap.querySelector('.nuda-hexin__chip');
const input = wrap.querySelector('input');

input.addEventListener('input', () => {
  const v = input.value.replace(/[^0-9a-f]/gi, '').slice(0, 6);
  input.value = v.toUpperCase();
  if (v.length === 6) chip.style.background = '#' + v;
});

.nuda-hexin {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 12px 6px 6px;
  background: rgba(0,0,0,.3);
  border: 1px solid rgba(255,255,255,.08);
  border-radius: 10px;
  transition: border-color .25s,box-shadow .25s;
}

.nuda-hexin:focus-within {
  border-color: #e4ff54;
  box-shadow: 0 0 0 3px rgba(228,255,84,.12);
}

.nuda-hexin__chip {
  width: 22px;
  height: 22px;
  border-radius: 6px;
  box-shadow: inset 0 0 0 1px rgba(255,255,255,.1);
  transition: background .35s;
}

.nuda-hexin__hash {
  color: #63636e;
  font-family: ui-monospace,SFMono-Regular,Menlo,monospace;
  font-size: 13px;
}

.nuda-hexin input {
  background: transparent;
  border: 0;
  outline: none;
  color: #fafafa;
  font-family: ui-monospace,SFMono-Regular,Menlo,monospace;
  font-size: 13px;
  font-weight: 600;
  letter-spacing: .08em;
  text-transform: uppercase;
  width: 84px;
}